The present invention relates to a wheel suspension for a motor vehicle, and in particular to an independent wheel suspension for passenger cars.
A wheel suspension is described in the IT journal A.M., 6/94, page 129. The wheel suspension described therein is designed as an independent wheel suspension in which an active adjustment of the wheel camber is provided, the camber adjustment being carried out by an actuator, or positioning member, that acts on one of the transverse suspension links that is directly coupled to the hub carrier, so that the wheel suspension geometry determined by the suspension links is changed overall in conjunction with the camber adjustment that is effected by adjustment of this suspension link. However, such a reciprocal influencing is in no way desirable, and it makes it virtually impossible to adjust the camber over large camber angle ranges because of the resulting effect on the wheel action.
A wheel suspension is described in German Patent Application No. DE 39 28 135 Al, in which the hub carrier is mounted using a ball joint in the intermediate carrier, whereby the mid-point of the ball joint lies within the wheel axis. The resulting swivelling capacity on all sides, which is controlled by actuators situated in the transition between the intermediate carrier and the hub carrier, is used to influence values significant for the vehicle driving performance, such as wheel camber, toe-in, etc., as a function of driving speed, transverse acceleration, steering angle, vehicle load etc. The order of magnitude of adjusting capabilities lies within the scope of that which is customary with regard to changes in camber, toe-in, toe-out, or steering angle on rear axles, due to driving performance, i.e., in the range of fairly small angle values.
The same is true for wheel suspensions described in German Patent Application No. DE 37 44 069 Al.
An object of the present invention is to provide a wheel suspension for motor vehicles, in particular an independent wheel suspension for passenger cars such that active camber adjustment makes it possible to use different tire properties and/or tire positions in relationship to the roadway in response to roadway characteristics and/or driving condition variables in order to improve the manageability of the vehicle without interference with the wheel suspension geometry.
The present invention provides a wheel suspension for motor vehicles, in particular independent wheel suspension for passenger cars, having a body-side wheel suspension, a hub carrier that is provided with an axle end holding the wheel, and having an intermediate carrier, which is positioned between the wheel suspension and hub carrier and upon which the hub carrier pivoted and against which the hub carrier is supported via an actuator acting in the vehicle transverse direction for active adjustment of the camber with reference to a pivot axis disposed in the vehicle longitudinal direction, characterized in that the pivot axis (9) of the hub carrier (8) running in vehicle longitudinal direction is vertically offset from the wheel axis, and a negative wheel camber on the order of magnitude of about 20-30xc2x0 can be set by pivoting the hub carrier (8) in such a way that the tread contact surface is moved to a tread area of the tire that is adjacent to the inside of the wheel.
The wheel suspension used can be in the form of a rigid axle, a semi-rigid axle (e.g., a torsion beam axle), an independent wheel suspension or other type of wheel suspension. Depending on the type of wheel suspension that is used, the elements of the wheel suspension that form the connecting elements on the body side, i.e., the axle body, the suspension links of the torsion beam axle or the suspension linksxe2x80x94rigid or non-rigid, for example leaf spring armsxe2x80x94of an independent wheel suspension are used as the body-side wheel suspension.
An embodiment according to the present invention, for example in the context of an independent wheel suspension, makes possible the use of independent wheel suspensions of known design and makes it possible, without intervening in the given wheel location or suspension geometry, to modify the camber angle of the wheel so that effects that previously had not been possible to implement can be carried out. This is especially true in connection with open loop and/or closed loop control strategies, in which the camber adjustment is performed as a function of the prevailing driving conditions and, if necessary, is performed as an automated adjustment in conformance therewith.
Thus, camber adjustment is useful with respect to the increase in transferrable lateral forcesxe2x80x94high negative camber on the outer, curve-side wheelsxe2x80x94it being possible to control the corresponding camber adjustment in response to the transverse acceleration, for example, by increasing the camber angle with increasing transverse acceleration. This offers special advantages in connection with tires that are supported on the roadway with different tread sections in relation to different camber angles, and in which these tread sections are adapted to the particular requirements with respect to the type of material and/or the tread profile.
The present invention makes it possible to implement strategies for improving driving safety by camber adjustment, for example by virtue of the fact that the corresponding influencing variables may be processed by a camber computer and input as the corresponding set point camber angles. This is done preferably on the four wheels of a multi-track vehicle, but at least on both wheels of an axle. Influencing variables to be considered are, e.g., the actual camber angle, the driving speed, the steering wheel angle and the steering wheel angle adjusting speed, the yaw rate, the road condition, and the given size of the wheel""s tread contact surface relative to the particular camber angle to be set.
On vehicles that are equipped with a steering computer, at least some of these state variables are also recorded for the steering computer. In this case, the transverse acceleration, the speed, the steering wheel angle, the adjusting speed of the steering wheel angle, the yaw rate, etc., are to be considered as influence variables. In independent wheel suspensions according to the present invention, whose camber angle can be actively adjusted, the actual camber angle and the particular set point camber angle being targeted have an influence on the respective set point steering angle. Accordingly, the camber computer and the steering computer can interlinked and the recording of additional characteristic quantities, in particular characteristic quantities from the braking system, also makes it possible to use the camber adjustment to improve the driving dynamics and driving stability of the vehicle.
This means the camber adjustment can be used to manage highly dynamic obstacle avoidance maneuvers, on one hand using the change in lateral stability that can be achieved by change in camber, and on the other hand using steering effects associated with the camber adjustment as such. In particular, stabilizing effects of this type, where the change in the camber position is used in the sense of four-wheel steering, can be used at high speeds.
In connection with braking maneuvers, especially emergency braking as can occur, for example in response to activation of the so-called xe2x80x9cbraking assistantxe2x80x9d, during response of anti-lock braking systems or the like, camber changes can be initiated to improve stability, in particular in connection with tires whose tread areas have different adhesion coefficients which are used in connection with the change in the camber as tread contact areas, whereby changing the size of the tread contact areas can also be used with the change in the camber.
In connection with tires in which differently-shaped tread areas are used depending on the camber that is set in each case, camber adjustment also offers the option of better managing weather-related driving difficulties, for example, by virtue of the fact that tread areas that are designed as tires equipped with cleats or studs can be brought into use by camber adjustment. In addition, the camber adjustment can also be activated in connection with driving dynamics systems, for example instead of, or in connection with, the measures initiated by such systems during wheel slip, e.g., braking intervention or the like.
The position of the hub carrier""s pivot axis according to the present invention, which is set higher than the wheel axis, provides substantial flexibility in camber positioning, since it can also be formed of links that are independent of each other, and it provides extensive options for arranging the actuator that acts between the hub carrier and the intermediate carrier. With the arrangement of the actuator between the hub carrier and intermediate carrier, intervention into the function and design of the suspension links can also be prevented, it being possible to use standard components in the form of hydraulic or electrical actuators, e.g., in the form of hydraulic control cylinders or electrical spindle drives, as actuators. Also, there is a fairly large number of options with regard to the positioning of the pivot axis within the scope of the present invention, so that even driven axles can be handled without difficulty, since the hub carrier can also have different structural forms, e.g., when viewed from the side, can have a sickle shape.
With respect to implementing a substantial modification to camber angle, according to the present invention a pivot axis may be positioned relatively high in relation to the wheel axis. To achieve corresponding track widening which also influences the steering performance, it can be effective to arrange the pivot axis according to the present invention with a certain tilt to the roadway plane, to achieve additional steering effects in connection with the camber adjustment independently of the wheel suspension on the body side and in particular the steering geometry determined by the wheel suspension links and the steering adjustment, in order to more or less compensate the steering effects associated with the camber adjustment. Even without considering the camber adjustment, this can make it possible to more or less maintain the standard steering performance or, conversely, to enhance, if necessary, the steering effects that are adjusted in conjunction with the camber adjustment, e.g., on axles that are not articulated.
If the wheel suspension according to the present invention is used in conjunction with articulated wheels, a vertical steering axis is also to be provided in accordance with the present invention either between the intermediate carrier and wheel suspension, or between the hub carrier and intermediate carrier.
In particular, it also proves to be particularly effective first to provide the wheel suspension with a system carrier that in turn holds the intermediate carrier, it being possible for the steering axis to be disposed between the intermediate carrier and the system carrier, or for the system carrier, as such, to be mounted so that it pivots.
In accordance with another embodiment within the scope of the present invention, a vertical steering axis is provided both between the intermediate carrier and the wheel suspension, as well as between the intermediate carrier and hub carrier, it being possible for these steering axes to also be configured in a crosswise arrangement, and it being advantageous to utilize the swivelling capability with respect to one of these steering axes, in particular the steering axis provided between the intermediate carrier and wheel suspension in conjunction with the intended steering, i.e., the steering input by the driver. In the meantime, the other steering axis, in particular the one between the intermediate carrier and the hub carrier, is used to make steering corrections, for example to adapt to steering movements caused by the wheel suspension or with regard to steering movements of the wheels, that are desirable from the perspective of driving dynamics. Depending on the arrangement of the steering axes, corresponding actuators will be provided that are arranged between the hub carrier and intermediate carrier, between the intermediate carrier and the wheel suspension and/or system carrier, or between the system carrier and wheel suspension.